\documentclass{article}
\usepackage[x11names, rgb]{xcolor}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\usetikzlibrary{snakes,arrows,shapes}
\usepackage{amsmath}
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\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{0pt}%
\usetikzlibrary{automata}%

\begin{document}
\pagestyle{empty}
%
%
%

\enlargethispage{100cm}
% Start of code
\begin{tikzpicture}[>=latex',join=bevel,]
\tikzstyle{every state}=[draw=blue!50,very thick,fill=blue!20]%
\node (q0) at (63bp,194bp) [state] {$\{q_{0}\}$};
  \node (q1) at (27bp,106bp) [state] {$\{q_{1}\}$};
  \node (q2) at (99bp,106bp) [state] {$\{q_{3}\}$};
  \node (q3) at (81bp,18bp) [state] {$\{q_{2}\}$};
  \draw [->] (q1) ..controls (33bp,73bp) and (39bp,52bp)  .. node[auto] {$\overline{a}$} (q3);
  \draw [->] (q0) ..controls (76bp,164bp) and (83bp,147bp)  .. node[auto] {$\tau$} (q2);
  \draw [->] (q0) ..controls (50bp,164bp) and (43bp,147bp)  .. node[auto] {$\tau$} (q1);
  \draw [->] (q2) ..controls (75bp,86bp) and (68bp,78bp)  .. (65bp,70bp) .. controls (62bp,61bp) and (63bp,52bp)  .. node[auto] {$\overline{c}$} (q3);
  \draw [->] (q2) ..controls (93bp,76bp) and (90bp,60bp)  .. node[auto] {$\overline{b}$} (q3);
  \draw [->] (q2) ..controls (108bp,78bp) and (110bp,65bp)  .. (107bp,54bp) .. controls (105bp,49bp) and (104bp,45bp)  .. node[auto] {$\overline{a}$} (q3);
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\end{tikzpicture}
% End of code

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\end{document}
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